Packers and bridge plugs serve as wellbore isolation devices. The main difference is that bridge plugs have no passage through a mandrel and are an absolute barrier, while packers have a mandrel passage and are usually associated with a valve to control flow between zones that are isolated from each other when the packer is set. In either case, these devices when set will have some differential pressure across them and the standard procedure for safe operation is to equalize the pressure across the packer or bridge plug first before release of the slip and seal assembly of the packer or bridge plug.
Very old designs involved a single movement of a mechanism to accomplish both tasks. This movement was in a single direction where the initial movement first equalized and continued movement in the same direction then released the slips and seal elements of the packer or plug. One potential problem with such a design is if the slips and seal of the packer or plug are released before the equalization has fully finished there could be a large enough force left on the packer to send it moving in a direction toward the surface which could send the tubular string attached to such packer moving out of the hole and create a dangerous condition. Accordingly subsequent designs sought to make the equalizing step discrete from the release step by using two discrete mechanisms and a grip tool that is initially blocked from grabbing the release mechanism as it initially grabs the equalizing mechanism by a plurality of dogs that act as travel stops. After the grip tool engages the equalizing mechanism and picks it up to equalize, a recess is presented opposite the dogs acting as a travel stop so that on a subsequent jarring down movement after equalization, the release mechanism is gripped because the dogs acting as a travel stop have gone into the recess so that a subsequent jarring up motion then releases the slips and sealing element of the packer. This system is described in detail in Bishop U.S. Pat. No. 8,322,413. Some problems inherent to this design are that wellbore debris could deposit near the dogs or their associated recess so that the packer release mechanism could not be gripped by the grip tool making release of the packer difficult if not impossible and dictating a milling operation for removal of the packer. Another issue with the Bishop '413 design was that once the lock ring below the slips was released to allow the packer to extend in a downhole direction for retraction of the upper and lower slips and sealing element there was still an issue as attempts were made to bring up the packer of the slips either not releasing their grip on the surrounding tubular or the slip cone not extending far enough away from the slips or getting pushed back under the slips as the packer was moved uphole causing the packer to get stuck.
To address these issues a grip tool was designed that eliminates the need for the dogs that act as a travel stop by having a grip tool that is initially only capable of reaching the equalizing mechanism. After equalization a further force applied in the same direction as for the equalizing results in a reconfiguration of the grip tool and locking the grip tool in the reconfigured position. In the locked reconfigured position, the grip tool is capable of engaging with the packer or plug release mechanism with an applied force. After such latching the applied force direction is reversed and the tool is released with an undermining of the ratchet lock used initially to hold the set position. In the event of a failure to release just relying on the stored potential energy of the set packer element an option is provided to re-engage the lower ratchet lock and transfer a downhole force to the lower slip cone to push the lower slip cone downhole from under the slips so as to provide another opportunity to get the slips and packer seal to release. An emergency release is provided to be able to remove the grip tool if the equalizing and release mechanisms fail to operate so that the grip tool and associated wireline can be removed from the borehole before fishing is attempted.
These and other features will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while keeping in mind that the full scope of the inventions described herein are to be determined by the appended claims.
Retractable slips are illustrated in U.S. Pat. No. 4,813,486 while retrievable bridge plugs and associated running tools are discussed in U.S. Pat. No. 5,366,010. Also relevant to telescoping tools are U.S. Pat. No. 6,349,770; completion method with telescoping perforation and fracturing tool U.S. Pat. No. 7,604,055; Downhole telescoping tool with radially expandable members WO 2011028812 and method and apparatus for accommodating telescoping action U.S. Pat. No. 3,354,950.